如何使用java流过滤对象？

Question

How to use the filter in java to filter the complete object. I am having an ArrayList that contains name and amount , I have another array of string that contains some string.

Now here how to filter and create a new ArrayList which contain only these two object which has arr elements.

I tried to use two methods .equals and .contains but it does not produce output.

List<Person> people = new ArayList<>();
people.add(new Person("Warren Buffett" , 90));
people.add(new Person("Jeff Bezos" , 180));
people.add(new Person("Bill Gates" , 140));
people.add(new Person("Mark" , 120));

String arr[]={"Mark" , "Bill Gates"};

List<Person> newPeople = people.stream().filter(person -> person.name.equals(arr))
List<Person> newPeople = people.stream().filter(person -> person.name.contains(arr)).collect(collectors.toList());

newPeople.forEach(person -> System.out.println(person.name));

Edit:

I should get the output as an array of an object that should contain Mark and Bill gates name and their amount

Answer 1

You cannot do this person.name.contains(arr) , rather you should be doing person.name.contains(arr[0]) OR person.name.contains(arr[1]) .
In order to do so, you might want to do nested iteration.

Answer 2

Below you can find working solution. Use streams to iterate by your args array to find first matching arg.

List<Person> newPeople = people.stream()
            .filter(person -> Stream.of(arr).anyMatch(s -> person.name.equals(s)))
            .collect(Collectors.toList());



newPeople.forEach(person -> System.out.println(person.name));
// Bill Gates
// Mark

Answer 3

You can convert the array to a list; then use the List.contains() to check if the person.name is available in that list .

First convert the array.

String arr[]={"Mark" , "Bill Gates"};
List<String> names = Arrays.asList(arr);

Now, use the List.contains()

List<Person> newPeople 
   = people.stream().filter(
                             person -> names.contains(person.name)).collect(Collectors.toList()
                           );

Below is the full method after the update.

public static void main(String[] args) {

    List<Person> people = new ArrayList<>();
    people.add(new Person("Warren Buffett" , 90));
    people.add(new Person("Jeff Bezos" , 180));
    people.add(new Person("Bill Gates" , 140));
    people.add(new Person("Mark" , 120));

    String arr[]={"Mark" , "Bill Gates"};
    List<String> names = Arrays.asList(arr);

    List<Person> newPeople = people.stream().filter(person -> names.contains(person.name)).collect(Collectors.toList());

    newPeople.forEach(person -> System.out.println(person.name));

}

Answer 4

So you want a new list containing only the Person instancences which names appears in arr? Try do this:

List<Person> newPeople = people.stream()
    .filter(person -> arr.contains(person.name))
    .collect(collectors.toList());

The lambda variable "person" is referring to a single object contained in the people list, not to the list itself. So when you use person.name.equals(...) or person.name.contains(...) your are calling those methods on a string. Doing the reverse, as in my example, will give you the desired result; if not, let know and we'll dig dipper

edit:

I was assuming arr was a List, so before using my code you should consider to do te following

List<String> names = Arrays.asList(arr);

And then

List<Person> newPeople = people.stream()
.filter(person -> names.contains(person.name))
.collect(collectors.toList());

Assuming you're having that array passed by something else, if you're creating it you could just create a list and skipping the array "step"